1. Field of the Invention
The invention relates to a method for the production of branched polymerizates P by means of at least two-stage polymerization of monomers M.sub.1 and M.sub.2, optionally in the presence of inert, non-aqueous solvents L, in which a mercaptan RM with an olefinic, radically polymerizable double bond is used as a molecular weight regulator in the first stage, as well as to uses for polymerizates P produced in this manner.
2. Description of the Background
Branched polymerizates, particularly comb polymers, are generally produced by polymerization of macromonomers, optionally with other monomers.
By definition, macromonomers represent polymers with an end group capable of polymerization, particularly a radically polymerizable end group, with mean molecular weights M.sub.w of 500 to about 10.sup.5 daltons, particularly from 2000 to 5.times.10.sup.4 daltons (for the determination of M.sub.w, see, for example, H. F. Mark et al., Encyclopedia of Polymer Science and Technology, 2nd Ed., Vol. 10, pages 1 to 19, J. Wiley, New York, 1989).
The production of macromonomers is described in detail in the literature (see, for example, P. F. Rempp, E. Franta, Adv. Polym. Sci. 58, 1 (1984); K. Albrecht, W. Wunderlich, Angew. Makromol. Chem. (Applied Macromolecular Chemistry) 145/146, 89-100 (1986); H. F. Mark et al., Encyclopedia of Polymer Science and Technology, 2nd Ed., Vol. 9, pages 195-204, J. Wiley (1989); T. Corner, Adv. Polym. Sci. 62, 95-141 (1984); P. Rempp and E. Franta. Adv. Polym. Sci. 58, 1-50 (1984); DE-PS 27 23 905 or U.S. Pat. No. 3,390,206).
Macromonomers are known to be obtainable via anionic and cationic "living polymerization," or via radical polymerization, where the end group capable of polymerization is usually introduced upon initiation or at the chain break, or by means of a subsequent chemical conversion. Another possibility for the production of macromonomers is offered by "Group Transfer Polymerization" (GTP; see, for example H. F. Mark et al., Encyclopedia of Polymer Science and Technology, 2nd Ed., Vol. 10, pages 1-19, J. Wiley, 1989).
A method for the production of comb polymers based on an acrylate which form elastomers, is described, for example, in DE-A 39 02 653, where the comb polymers are composed of 95 to 50% by weight of acrylate monomers and at 5 to 50% by weight of macromonomers consisting of a polyvinyl unit with a vinyl end group, where the polyvinyl unit consists of monomer units selected from the group of acrylates, methacrylates and styrenes, optionally substituted, as well as having a glass transition temperature T.sub.g of at least 60.degree. C. and a mean molecular weight of 500 to 10.sup.5 daltons.
EP-A 357 036 comprises a method for the production of comb polymers in which macromonomers with vinyl end groups and mean molecular weights between 3000 and 50000 daltons are mixed with vinyl monomers and a polymerization initiator, in a solvent which dissolves the macromonomers well and has a solubility in water of more than 10% by weight at 30.degree. C., and where the resulting mixture is subjected to aqueous suspension polymerization.
In DE-A 40 10 893, a method for the production of acrylic elastomers is described, where alkyl acrylates and alkoxyalkyl acrylates are polymerized in the presence of an organic peroxide with a non-conjugated double bond as the polymerization initiator, as well as in the presence of molecular weight regulators containing sulfur and having non-conjugated double bonds.
In EP-A 520 668, a two-stage process in aqueous emulsion for the production of branched polymerizates is described, where in the first stage, macromonomers with end vinyl groups are formed by the polymerization of ethylene-unsaturated monomers in the presence of mercaptans with olefinic groups, which macromonomers are converted to branched copolymerizates with other ethylene-unsaturated monomers in the second stage.
The state of the art methods for the production of branched polymerizates which have macromonomer units as comonomer units mostly comprise separate production and isolation of the macromonomers, before they are converted to branched end products by means of polymerization, optionally with other monomers.
While EP-A 520 668 offers a method for the production of branched polymerizates by means of copolymerization of macromonomers with other monomers, in which the macromonomers produced in the intermediary stage are subsequently directly polymerized further, this method has a disadvantage that it is carried out in aqueous emulsion. Depending on the area of use of the branched polymerizates, this requires rather complicated processing of the resulting polymer dispersion to remove the polymer emulsifiers. This is particularly true when branched polymerizates are used as thermoplastic elastomers with high transparency. The method disclosed in EP-A 520 668 is further limited in that comb polymerizates are produced almost exclusively because of the reactivity difference between the unsaturated group of the monomers used for the production of the macromonomers and the olefinic group of the mercaptans used as molecular weight regulators, which practically prevents inclusion of the mercaptans into the macromonomers via polymerization of the unsaturated group.
Thus, a need exists for a method for the production of branched polymerizates which is simple to carry out and allows easy isolation of the branched polymerizates.